Palangkaraya. A conservation group in Central Kalimantan, the Borneo Orangutan Survival Foundation, or BOS, has since 1991 rescued more than 2,200 orangutans.

BOS is the biggest orangutan rehabilitation group in the world, currently looking after 700 animals, preparing them at its Nyaru Menteng Orangutan Rescue Center to return to their natural habitat.

"We are the biggest, but we are not proud of it, as it shows there's a big environmental problem," BOS Foundation chief executive Jamartin Sihite said.

The foundation's 400 staff members rescue and rehabilitate orangutans that have been orphaned by poachers, sold at illegal markets or had lost their habitat to palm oil plantations, wildfires and degradation of rainforests.

Orangutans learn survival skills from their mothers. Since many of them were orphaned at an early age, at Nyaru Menteng they learn the skills from their human caretakers. The process can take up to several years.

Young orangutans play with their keepers at the Nyaru Menteng orangutan rescue center on Monday (01/05). (B1 Photo/Danung Arifin)

Orphan orangutans are increasingly common as palm oil plantations destroy their habitats and poachers hunt them for trade. (B1 Photo/Danung Arifin)

Orangutans learn survival skills from their mothers. Since many of them were orphaned at an early age, at Nyaru Menteng they learn the skills from their human caretakers. The process can take up to several years. (B1 Photo/Danung Arifin)